Gravitational lensing technique unveils supermassive black hole pairs

Supermassive black hole binaries form naturally when galaxies merge, but scientists have only confidently observed a very few of these systems that are widely separated. Black hole binaries that closely orbit each other have not yet been measured. In a paper published today in Physical Review Letters, the researchers suggest hunting down the hidden systems by searching for repeating flashes of light from individual stars lying behind the black holes as they are temporarily magnified by gravitational lensing as the binary orbits.